The present invention relates to apparatus and method for the elimination of nitrogen oxides (NOx) from combustion waste gases, particularly for deoxidizing the nitrogen oxides by injecting ammonia gas (NH.sub.3) therein, in the presence of a metallic catalyst.
Discharge of the combustion waste gases into the atmosphere without treatment is highly objectionable, because the nitrogen oxides are corrosive and act as atmospheric pollutants. Thus, it is desirable to treat such combustion waste gases in order to eliminate the nitrogen oxides prior to their being discharged into the atmosphere. The usual approach to such treatment is to catalytically react the combustion waste gases containing nitrogen oxides with a reducing gas, such as methane, hydrogen or ammonia.
It is well known to conduct the combustion waste gases and ammonia gas for deoxidizing the nitrogen oxides into a reaction tower containing catalysts to promote the deoxidation. Heretofore, a layer of catalysts has been fixedly disposed in the reaction tower and various metallic sulfides, metallic oxides and metallic alloys have been employed as the catalysts. Generally, however, the combustion waste gases contain a large quantity of dust and uncombustible materials, so that the dust and uncombustible materials attach themselves to the catalysts to worsen the catalytic properties of the catalysts.